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Aqueduct Stenosis

Summary

  • Narrowing of the Sylvian aqueduct can cause impaired CSF outflow resulting in either acute or chronic hydrocephalus
  • Can be caused by a congenital web but may also be caused by midbrain tumours, haemorrhage or infection

Cases

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  • A 40-year-old patient had an MRI scan due to chronic but increasing headaches
  • MRI showed a focal filling defect in the inferior sylvian aqueduct
  • CSF flow studies showed normal biphasic flow indicating a stenosis rather than an obstruction

Pathophysiology

  • Narrowing or obstruction of the cerebral Sylvian aqueduct resulting causing impaired CSF drainage and increase intraventricular pressure
  • Typically a longstanding lesion, hydrocephalus is usually compensated (i.e., no periventricular oedema or sulcal effacement)

Demographics

  • Most common cause of congenital hydrocephalus
  • Incidence: 0.5-1 per 1000 live births
  • Male predominance (2:1 ratio)

Diagnosis

  • Clinical presentation (headaches, vomiting) and clinical findings (papilloedema, bulging fontanelle in infancy) usually relate to raised intracranial pressure

Imaging

  • Dilated lateral and third ventricles
  • Normal or small fourth ventricle
  • Possible periventricular hypoattenuation (CT) or hyperintensity (T2-weighted imaging) due to oedema
  • High resolution T2-weighted imaging (e.g., CISS or FIESTA) usually indicated to identify small aqueduct web
  • CSF flow studies (midline sagittal and axial at level of Sylvian aqueduct) can be considered to qualitatively or quantitatively assess CSF flow across stenosis

Treatment

  • Surgery considered when symptomatic or increasing ventriculomegaly:
  • Endoscopic third ventriculostomy (ETV): preferred first-line treatment
  • Ventriculoperitoneal (VP) shunt: alternative if ETV fails or is contraindicated
Differential Diagnosis Differentiating Feature
Communicating Hydrocephalus All ventricles enlarged, including 4th ventricle
Normal Pressure Hydrocephalus Typically affects older adults; triad of gait disturbance, urinary incontinence, and dementia